Improvements relating to gas separation

ABSTRACT

A method of purifying gaseous mixtures, for example ternary or quaternary gaseous mixtures, using a sorbent media comprising two or more sorbent materials. The method involves obtaining a target gas from a gaseous composition comprising the target gas, a first gas and a second gas, and optionally further gases by contacting the gaseous composition with the sorbent media to remove at least some of the first gas and at least some of the second gas from the gaseous composition. The sorbent media comprises at least a first sorbent material and a second sorbent material; wherein the first sorbent material has a higher adsorption selectivity for the first gas than for the target gas; and wherein the second sorbent material has a higher adsorption selectivity for the second gas than for target gas. The method may be particularly useful for the separation of pure ethylene, methane or propylene from such gaseous mixtures. A sorbent media and an apparatus for obtaining a target gas from such a gaseous composition are also disclosed.

The present invention relates to a method of obtaining a target gas froma gaseous composition comprising the target gas and at least two othergases. The present invention also relates to the use of a sorbentmaterial for obtaining the target gas from such a gaseous compositionand to an apparatus for carrying out said methods and uses. Inparticular, the present invention relates to energy efficient methods ofpurifying hydrocarbons such as ethylene, propylene and methane.

At present, purification of commodities consumes about 15% of globalenergy. Commodities include agricultural products, fuels and metals andthe demand for such commodities has been projected to triple by 2050.For example, ethylene and propylene are some of the world's mostimportant chemicals—the production of ethylene (C₂H₄) and propylene(C₃H₆) alone accounts for 0.3% of global energy use. Over 60% of rawethylene is used in the plastics industry, with industrial uses ofethylene including polymerisation to form poly(ethylene) amongst others.

Polymerisation-grade (defined as being above 99.9% purity) ethylene isproduced by a separation of downstream C₂ hydrocarbon gas mixturesproduced by a steam cracking process. Such gas mixtures comprisehydrocarbons, notably other C₂ hydrocarbons such as acetylene (C₂H₂) andethane (C₂H₆), as well as trace impurities such as carbon dioxide (CO₂).Acetylene is removed from such gas mixtures either via catalytichydrogenation or solvent extraction. Catalytic hydrogenation involvesthe use of a metal catalyst at high temperatures and pressures, whilesolvent extraction requires a significant solvent volume and a largeoperating unit. Ethane is typically removed using cryogenicdistillation. However, all of the aforementioned methods involve highenergy consumption and costly processes. There is therefore a need todevelop less energy-intensive methods of obtaining high purity ethylenefrom gas mixtures comprising other hydrocarbon gases and impurities.

Therefore to obtain polymer-grade ethylene in a one-step process it isnecessary to remove both acetylene and ethane, and any other traceimpurities, from an impure ethylene gas. In principle, this could beachieved in several ways, for example using chemical transformation,chemisorption, extraction or membrane-based technologies. However, allof these approaches have drawbacks. For example, the methods may makeuse of expensive raw materials, require specialist equipment or takesignificant amount of time. In any case, it has not yet proven to bepossible to carry out such a purification of ethylene in one-step usingthese methods.

The use of physisorbents for the purification of gaseous hydrocarbonssuch as ethylene could significantly improve the efficiency of theirproduction. Physisorbents are able to physically bond to gas moleculesdue to the presence of weak, long range van der Waals interactions.Known physisorbents typically comprise cavities or pores to facilitatesuch adsorption and examples include zeolites and porous metal-organicframeworks. However, it does not appear to be possible to simultaneouslyremove acetylene, ethane and other trace impurities from ethylene usinga known physisorbent material, due to the similarity in size andchemistry of C₂ hydrocarbon molecules, which limits the selectivity ofmost physisorbents for each of acetylene, ethane and other traceimpurities over ethylene. This is further complicated when traceimpurities such as carbon dioxide are present as the physisorbent wouldneed a strong affinity towards acetylene, ethane and carbon dioxide overethylene.

It is an aim of the present invention to provide a method, use orapparatus that addresses at least one disadvantage of the prior art,whether identified here or elsewhere, or to provide an alternative toexisting methods, uses or apparatus. For instance, it is an aim ofembodiments of the present invention to provide a method of obtainingethylene from a gaseous composition comprising ethylene and at least twoother gases.

According to example embodiments, there is provided a method, use andapparatus as set forth in the appended claims. Other features of theinvention will be apparent from the dependent claims, and thedescription which follows.

According to a first aspect of the present invention, there is provideda method of obtaining a target gas from a gaseous composition comprisingthe target gas, a first gas and a second gas, the method comprising thestep of contacting the gaseous composition with a sorbent media toremove at least some of the first gas and at least some of the secondgas from the gaseous composition; wherein the sorbent media comprises afirst sorbent material and a second sorbent material; wherein the firstsorbent material has a higher adsorption selectivity for the first gasthan for the target gas; and wherein the second sorbent material has ahigher adsorption selectivity for the second gas than for the targetgas.

The method of this first aspect may be considered to be a method ofincreasing the concentration of a target gas in the gaseous compositioncomprising the target gas, the first gas and the second gas, the methodcomprising contacting the gaseous composition with the sorbent media.The method involves increasing the concentration of the target gas inthe (starting) gaseous composition, by removal of at least some of thefirst gas and the second gas, suitably substantially all of the firstgas and the second gas.

The first and second gases are different to each other and are not thesame as the target gas. Therefore the gaseous composition comprises thetarget gas and at least two different other gases. The first and secondgases may be considered to be impurity gases. Therefore the first gasmay be referred to as a first impurity gas and the second gas may bereferred to as a second impurity gas. The gaseous composition comprisingthe target gas may therefore be considered to be an impure gaseouscomposition and the method of this first aspect may be considered toproduce a target gas with an increased purity. The method of this firstaspect may therefore be considered to be a method of purifying a targetgas.

The target gas is suitably ethylene, propylene, propane or methane.

The sorbent media is suitably a solid sorbent media, suitably a solidmaterial which is stable to allow mechanical handling. Suitably thesorbent media is provided as a bed, for example on a suitable supportmaterial/structure. The sorbent media comprises a first sorbent materialand a second sorbent material. The first and second sorbent materialsare different to each other, but may be structurally related or fromwhat is considered to be the same class of sorbent materials. Forexample, the first and/or the second sorbent material may be solidmicroporous sorbent materials, suitably hybrid porous materials orhybrid ultramicroporous materials (HUMs). Such sorbent materials may bealternatively defined as metal organic materials (MOMs), metal organicframeworks (MOFs) or porous coordination polymers (PCPs). The sorbentmaterials may be known as physisorbent materials.

The sorbent media may comprise the first and second sorbent materials,and any further sorbent materials, in discrete sections, for examplediscrete sections arranged in series on a bed wherein the gaseouscomposition contacts the first sorbent material as it passes over orthrough the sorbent media and then contacts the second sorbent media, orvice versa. In some embodiments, the sorbent media may comprise thefirst and second sorbent materials, and any further sorbent materials,in a mixture, for example wherein the first and second sorbent materialsare randomly distributed throughout the sorbent media. In suchembodiments, the gaseous composition would contact both the first andsecond sorbent materials at the same time and throughout the passing ofthe gaseous mixture over or through the sorbent media. Suitably thesorbent media may comprise the first and second sorbent materials, andany further sorbent materials, in discrete sections arranged in series.The inventors have found that the method of obtaining a target gas froma gaseous composition comprising the target gas can be more efficient ifthe different sorbent materials are in discrete sections arranged inseries, rather than being mixed.

The contacting of gaseous composition with a sorbent media to remove atleast some of the first gas and at least some of the second gas from thegaseous composition is carried in one step or operation, for example ina single chamber through which the gaseous composition is passed in themethod. The contacting of the gaseous composition with the first sorbentmaterial in the sorbent media is carried out at the same time and/orwithin the same step or operation as the contacting of the gaseouscomposition with the second sorbent material in the sorbent media,rather than during separate steps or operations or in separate chambers.

In the method of this first aspect, the first sorbent materialselectively adsorbs the first gas and the second sorbent materialselectively adsorbs the second gas. Therefore, at least two separate gasadsorption processes are occurring in the method when the gaseouscomposition contacts the sorbent media.

By appropriate selection of the first and second sorbent materials, theinventors have found that a target gas, for example ethylene, can beadvantageously obtained or purified from a gaseous compositioncontaining the target gas and at least two other different gases, forexample acetylene, ethane and/or carbon dioxide, in a single operationin the method of this first aspect by contacting the gaseous compositionwith the sorbent media to remove the first and second gases. The targetgas may be obtained in greater purity than known methods wherein asingle sorbent material is used. For example, ethylene may be obtainedin a more cost effective and/or energy efficient manner compared to theknown, multi-step methods of purifying ethylene discussed above.

According to a second aspect of the present invention, there is provideda use of a sorbent media comprising a first sorbent material and asecond sorbent material, to increase the concentration of a target gasin a gaseous composition comprising the target gas, a first gas and asecond gas; wherein the sorbent media selectively adsorbs the first gasand the second gas over the target gas.

Preferred features of the first and second aspects of the invention willnow be described.

The gaseous composition comprises a target gas. Suitably the target gasis a hydrocarbon, such as a hydrocarbon which is typically contaminatedwith C₂ hydrocarbons after production and requires purification byremoval of said C₂ hydrocarbons. The target gas is suitably a C₁₋₄hydrocarbon. The present invention may be particularly effective in thepurification of ethylene, propylene, propane and methane. The target gasmay be selected from ethylene, propylene, propane and methane. Thepresent invention may be particularly effective in the purification ofethylene and methane. The target gas may be selected from ethylene andmethane.

The gaseous composition comprising a target gas, a first gas and asecond gas is suitably obtained from a petrochemical process. Suitablythe gaseous composition comprises hydrocarbons, suitably C₂hydrocarbons. Suitably the gaseous composition comprises ethylene (C₂H₄)and other C₂ hydrocarbons, for example acetylene (C₂H₂) and ethane(C₂H₆). The gaseous composition may comprise trace gases, for examplecarbon dioxide (CO₂), carbon monoxide (CO) and water (H₂O).

Suitably the first gas is acetylene. Suitably the second gas is ethane.Suitably the first gas is acetylene and the second gas is ethane.

In some embodiments, the target gas is ethylene. In such embodiments,the gaseous composition suitably comprises ethylene, acetylene andethane. The gaseous composition may comprise a third gas, suitablycarbon dioxide. In such embodiments the gaseous composition may compriseethylene, acetylene, ethane and carbon dioxide. The gaseous compositionis suitably a composition produced industrially from which ethylene iscurrently extracted by known methods.

In some embodiments, the gaseous mixture is a ternary gaseous mixture,suitably consisting essentially of or consisting of ethylene, acetyleneand ethane. In some embodiments, the gaseous mixture is a quaternarygaseous mixture, suitably consisting essentially of or consisting ofethylene, acetylene, ethane and carbon dioxide.

Suitably the gaseous composition comprises at least 20 wt % ethylene,suitably at least 25 wt %, for example at least 30 wt % ethylene.

Suitably the gaseous composition comprises up to 90 wt % ethylene,suitably up to 80 wt %, for example up to 75 wt % ethylene.

Suitably the gaseous composition comprises from 20 to 90 wt % ethylene,suitably from 25 to 80 wt %, for example from 30 to 75 wt % ethylene.

Suitably the gaseous composition comprises at least 0.001 wt %acetylene, suitably at least 0.01 wt %, for example at least 0.1 wt %acetylene.

Suitably the gaseous composition comprises up to 5 wt % acetylene,suitably up to 2 wt %, for example up to 1.5 wt % acetylene.

Suitably the gaseous composition comprises from 0.001 to 5 wt %acetylene, suitably from 0.01 to 4 wt %, suitably from 0.05 to 3 wt %suitably from 0.1 to 2 wt %, for example from 0.5 to 1.5 wt % acetylene.

Suitably the gaseous composition comprises at least 20 wt % ethane,suitably at least 25 wt %, for example at least 30 wt % ethane.

Suitably the gaseous composition comprises up to 70 wt % ethane,suitably up to 65 wt %, for example up to 60 wt % ethane.

Suitably the gaseous composition comprises from 20 to 70 wt % ethane,suitably from 25 to 65 wt %, for example from 30 to 60 wt % ethane.

Suitably the gaseous mixture comprises from 30 to 75 wt % ethylene, from0.1 to 2 wt % acetylene and from 30 to 60 wt % ethane.

In embodiments wherein the gaseous mixture comprises carbon dioxide, thegaseous composition suitably comprises at least 5 wt % carbon dioxide,suitably at least 10 wt %, for example at least 20 wt % carbon dioxide.

The gaseous composition suitably comprises up to 60 wt % carbon dioxide,suitably up to 50 wt %, for example up to 40 wt % carbon dioxide.

The gaseous composition suitably comprises from 10 to 60 wt % carbondioxide, suitably from 15 to 50 wt %, for example from 20 to 40 wt %carbon dioxide.

Suitably the gaseous mixture comprises from 25 to 75 wt % ethylene, from0.1 to 2 wt % acetylene, from 25 to 60 wt % ethane and from 15 to 50 wt% carbon dioxide.

In some embodiments, the target gas is methane. In such embodiments, thegaseous composition suitably comprises methane, acetylene and ethane.The gaseous composition may comprise a third gas, suitably carbondioxide. In such embodiments the gaseous composition may comprisemethane, acetylene, ethane and carbon dioxide. The gaseous compositionis suitably a composition produced industrially from which methane iscurrently extracted by known methods.

In such embodiments, the gaseous mixture may be a ternary gaseousmixture, suitably consisting essentially of or consisting of methane,acetylene and ethane. In such embodiments, the gaseous mixture may be aquaternary gaseous mixture, suitably consisting essentially of orconsisting of methane, acetylene, ethane and carbon dioxide.

In such embodiments, the methane may be present in the gaseouscomposition in the amounts described above for ethylene. The acetylene,ethane and carbon dioxide, when present, may be present in the amountsdescribed above.

The method and use of the present invention involves contacting thegaseous composition with the sorbent media. This suitably involvespassing the gaseous composition through a chamber comprising the sorbentmedia, suitably wherein the sorbent media is provided as a fixed bed.Contacting the gaseous composition with the sorbent media allows atleast a part of the first gas and the second gas, and any third orfurther gases present, to be adsorbed onto and/or into the sorbentmaterials which make up the sorbent media. Suitably the first and secondgases are adsorbed onto an inner surface of the first and second sorbentmaterials, respectively, suitably an inner surface of the pores of thesorbent materials. This removes at least some of (and suitablysubstantially all of) the first gas and the second gas, and any third orfurther gases present, from the gaseous composition, leaving anincreased concentration of ethylene in the gaseous composition aftercontact with the sorbent media compared with before contact with thesorbent media.

The sorbent media comprises the first sorbent material and the secondsorbent material. The first sorbent material has a higher adsorptionselectivity for the first gas than for the target gas. Suitably thefirst sorbent material has a higher adsorption selectivity for the firstgas than for the target gas and the second gas, and suitably also forany third or further gas present. The first gas is suitably acetyleneand therefore the first sorbent material suitably has a higheradsorption selectivity for acetylene than for the target gas, suitablyethylene or methane. The first sorbent material suitably has a higheradsorption selectivity for acetylene than for the target gas and ethane.The first sorbent material suitably has a higher adsorption selectivityfor acetylene than for the target gas, ethane and carbon dioxide.

The second sorbent material has a higher adsorption selectivity for thesecond gas than for the target gas. Suitably the second sorbent materialhas a higher adsorption selectivity for the second gas than for thetarget gas and the first gas, and suitably also for any third or furthergas present. The second gas is suitably ethane and therefore the secondsorbent material suitably has a higher adsorption selectivity for ethanethan for the target gas, suitably ethylene and methane. The secondsorbent material suitably has a higher adsorption selectivity for ethanethan for the target gas and acetylene. The second sorbent materialsuitably has a higher adsorption selectivity for ethane than for thetarget gas, acetylene and carbon dioxide.

Suitably the first and second sorbent materials, and any third orfurther sorbent materials present, may be selected from ultramicroporousmaterials such as hybrid ultramicroporous materials (HUMs). Suitableultramicroporous materials comprise a three-dimensional lattice of metalspecies (M) and linker groups. Suitably the metal species (M) are linkedtogether in a first and second dimension by first linker groups (L¹) andare linked together in a third dimension by second linker groups (L²) toform the three-dimensional lattice.

The First Sorbent Material

The first sorbent material is suitably an ultramicroporous materialwherein one of L¹ and L² is an organic linker group and the other of L¹and L² is an inorganic linker group, which has a higher adsorptionselectivity for acetylene than for ethylene and ethane, and suitablycarbon dioxide.

Suitably the first sorbent material has the chemical formula:M(L¹)2(L²), which may additionally comprise anions such as halogen ions,where appropriate. Therefore the first sorbent may have the formulaM_(x)(L¹)₂(L²)Y_(z) wherein x is an integer from 1 to 3, suitably 1 or2, Y is an anion, suitably a halogen anion, and z is an integer from 0to 3, suitably 1 or 2. Suitably the metal species (M) are transitionmetal atoms or ions. Suitably the metal species (M) are first rowtransition metal atoms or ions. Suitably the metal species (M) areselected from atoms or ions of Co, Cu, Zn and Ni. Suitably the metalspecies (M) are Co ions, Cu ions or Ni ions, suitably Co²⁺, Cu²⁺ ions orNi²⁺ ions. Suitably the metal species (M) are Cu ions, suitably Cu²⁺ions. In some embodiments the metal species (M) are Ni ions, suitablyNi²⁺ ions, or Co ions, suitably Co²⁺. Suitably all metal species (M) inthe hybrid porous material are the same.

In the first sorbent material, the metal species (M) are linked togetherin a first and second dimension by first linker groups (L¹). One of L¹and L² is an organic linker group and the other of L¹ and L² is aninorganic linker group. In other words either the first linker groups(L¹) are organic linkers and the second linker groups (L²) are inorganiclinkers, or the first linker groups (L¹) are inorganic linkers and thesecond linker groups (L²) are organic linkers. Therefore the firstlinker groups (L¹) may be organic linkers or inorganic linkers.Alternatively, in materials comprising halide anions (z=1 to 3), L¹ andL² can be both organic linkers.

Suitably the first linker groups (L¹) are organic linkers. Preferablythe first linker groups (L¹) comprise at least two donor atoms. Donoratoms are atoms present within the linker group which have a loneelection pair which can be donated, for example in the formation of ametal-ligand complex. This lone electron pair is suitably donated to themetal species on formation of the hybrid porous material. The donoratoms may be charged or neutral species, for example a donor atom may infact be present as an ion such as an oxygen atom of a carboxylatespecies.

Suitably the donor atoms in the organic linkers are selected fromhalogens, oxygen and nitrogen. A suitable organic linker may compriseN-oxide groups which provide an oxygen donor atom. The two or more donoratoms may each be the same or different.

Suitably the donor atoms are selected from oxygen and nitrogen.Preferably all the donor atoms are nitrogen.

Suitably the first linker groups (L¹) are nitrogen ligands comprising atleast two donor atoms which are nitrogen atoms. Suitably the at leasttwo nitrogen atoms each comprise a lone pair of electrons suitable forbinding to a metal species. Therefore the nitrogen ligands are suitablytwo-connected nitrogen ligands. By “two-connected” we mean the nitrogenligand is capable of binding to two different metal species (M) in thehybrid porous material. In preferred embodiments the lone pairs ofelectrons on the two nitrogen atoms are in orbitals orientated away fromeach other at an angle capable of forming a lattice, for example anangle greater than 90°, for example an angle of approximately 120° or anangle of approximately 180°.

Suitably the two nitrogen atoms in the two-connected nitrogen ligandsare separated by from 2.5 to 20 Å, for example separated by from 2.5 to10 Å or from 10 to 20 Å.

Suitably the first linker groups (L¹) are two-connected nitrogenligands. Preferred two-connected nitrogen ligands comprise at least onenitrogen-containing heterocycle. In some embodiments the two-connectednitrogen ligand may be a nitrogen-containing heterocycle comprising twonitrogen atoms each having a lone pair of electrons, for examplepyrazine.

In some embodiments the two-connected nitrogen ligand comprises twonitrogen-containing heterocycles. The two nitrogen-containingheterocycles may be linked together by a bond. One such preferredtwo-connected nitrogen ligand is 4,4′-bipyridine.

Alternatively, the two nitrogen-containing heterocycles may be linkedtogether by a spacer group, for example acetylene. One such preferredtwo-connected nitrogen ligand is 4,4′-bipyridylacetylene. Suitably thefirst linker groups (L¹) are two-connected nitrogen ligands having theformula (L2N):

wherein R¹ is an optionally substituted linker group.

R¹ may be a heteroatom, a group of connected heteroatoms or a groupcomprising heteroatoms. For example R¹ may be a —N═N— group.

R¹ may be a hydrocarbyl group. The hydrocarbyl group may comprise acyclic group. The hydrocarbyl group may comprise an aromatic cyclicgroup. The hydrocarbyl group may comprise a heterocyclic group.

As used herein, the term “hydrocarbyl” is used in its ordinary sense,which is well-known to those skilled in the art. Specifically, it refersto a group having predominantly hydrocarbon character. Examples ofhydrocarbyl groups include:

(i) hydrocarbon groups, that is, aliphatic (which may be saturated orunsaturated, linear or branched, e.g., alkyl or alkenyl), alicyclic(e.g., cycloalkyl, cycloalkenyl) substituents, and aromatic-,aliphatic-, and alicyclic-substituted aromatic substituents, as well ascyclic substituents wherein the ring is completed through anotherportion of the molecule (e.g., two substituents together form a ring);

(ii) substituted hydrocarbon groups, that is, substituents containingnon-hydrocarbon groups which, in the context of this invention, do notalter the predominantly hydrocarbon nature of the substituent (e.g.,halo (especially chloro and fluoro), hydroxy, alkoxy, keto, acyl, cyano,mercapto, alkylmercapto, amino, alkylamino, nitro, nitroso, andsulphoxy);

(iii) hetero substituents, that is, substituents which, while having apredominantly hydrocarbon character, in the context of this invention,contain other than carbon in a ring or chain otherwise composed ofcarbon atoms. Heteroatoms include sulphur, oxygen, nitrogen, andencompass substituents as pyridyl, furyl, thienyl and imidazolyl.

Suitable two-connected nitrogen ligands may be selected from pyrazine,4,4′-bipyridine and from 4,4′-bipyridylacetylene and compounds (LA) to(LFF):

Suitably the first linker groups (L¹) are two-connected nitrogen ligandsselected from pyrazine, 4,4′-bipyridine and 4,4′-bipyridylacetylene.Suitably the first linker groups (L¹) are selected from4,4′-bipyridylacetylene and 4,4′-bipyridine. Suitably the first linkergroups (L¹) is 4,4′-bipyridylacetylene.

Suitably all first linker groups (L¹) in the hybrid porous material arethe same.

The metal species (M) are linked together in a first and seconddimension by the first linker groups (L¹). Suitably the first and seconddimensions are substantially perpendicular to one another. Suitably thefirst linker groups (L¹) link together the metal species (M) to form atwo-dimensional layer having a square planar repeating unit of formula(I):

The metal species (M) are linked together in a third dimension by secondlinker groups (L²) to form a three-dimensional lattice. Suitably thesecond linker groups (L²) are capable of forming an interaction betweentwo different metal species. Typically the metal species form atwo-dimensional layer with first linker groups (L¹), for example atwo-dimensional layer of square planar repeating units, for example offormula (I).

Suitably the second linker groups (L²) form an interaction with twodifferent metal species in two different layers. Suitably the secondlinker groups (L²) are capable of forming interactions with twodifferent atoms or ions of metal species (M) in order to form athree-dimensional lattice. For example the second linker groups (L²) arecapable of forming interactions with two different atoms or ions ofmetal species (M) which are orientated at an angle to each other ofgreater than 90°, for example an angle of approximately 120° or an angleof approximately 180°.

Suitably the second linker groups (L²) are inorganic linkers. Suitablyeach second linker group (L²) includes at least two donor atoms.Suitable donor atoms include halogens, oxygen, nitrogen and sulphur.Preferred donor atoms of the second linker groups (L²) are halogens,especially chlorine or fluorine, preferably fluorine. Suitably thesecond linker groups (L²) comprise at least one halogen or chalcogen(Group VIA) atom. Preferably the second linker groups (L²) comprise atleast one fluorine or oxygen atom.

Suitably the second linker groups (L²) are inorganic compoundscomprising at least one fluorine atom. Suitably the second linker groups(L²) are charged, suitably anions. Suitably the second linker groups(L²) are inorganic anions comprising at least one fluorine atom.Preferably the second linker groups (L²) comprise at least two halogenatoms. Preferably the second linker groups (L²) comprise at least twofluorine atoms.

Suitably the second linker groups (L²) are compounds of formula AX_(n)^(Y−), wherein X is selected from F or Cl, n is an integer from 2 to 6,y is an integer from 0 to 2 and A is selected from Si, Ti, Sn, Zr or Ge.Suitably n is an integer from 4 to 6. Preferably n is 6. Preferably y is2. Suitably X is F. Suitably the second linker groups (L²) are selectedfrom SiF₆ ²⁻, TiF₆ ²⁻, SnF₆ ²⁻, ZrF₆ ²⁻ and GeF₆ ²⁻. Suitably the secondlinker groups (L²) are selected from SiF₆ ²⁻, TiF₆ ²⁻ and SnF₆ ²⁻.Suitably the second linker groups (L²) are ions of TiF₆ ²⁻.

In some embodiments, the second linker groups (L²) are organic linkerswherein each second linker group (L²) includes at least two donor atoms.Suitable donor atoms include oxygen, nitrogen and sulphur. Preferreddonor atoms of the second linker groups (L²) are oxygen atoms,especially from carboxylate groups, or nitrogen atoms, especially fromazolate groups. Suitably the second linker groups (L²) comprise at leastchalcogen (Group VIA) atom or pnictogen (Group VA). Preferably thesecond linker groups (L²) comprise at least oxygen atom or nitrogenatom.

In such embodiments, the second linker groups (L²) may be carboxylicacids, for example di-carboxylic acid compounds or ions. Such secondlinker groups (L²) may be selected from chiral or racemic tartaric acid,malic acid, succinic acid, fumaric acid, 2,3-dibromosuccinic acid,aspartic acid, 1,4-benzenedicarboxylic acid and 1,3-benzenedicarboxylicacid. The second linker group (L²) may be L-tartaric acid (L-tart).

Suitably all second linker groups (L²) in the hybrid porous material arethe same.

Suitably the second linker groups (L²) link the metal species (M) ofdifferent two dimensional layers having a repeating unit of formula (I)to form the three-dimensional lattice. Suitably the three-dimensionallattice of metal species (M) and linker groups has a cubic latticestructure, suitably a primitive cubic lattice structure. Suitably thethree-dimensional lattice of metal species (M) and linker groups (L¹ andL²) comprises the repeating unit (unit cell) of formula (II):

Suitably the three-dimensional lattice of metal species (M) and linkergroups consists essentially of repeating units of formula (II).

Suitably the metal species (M) are selected from Co²⁺ and/or from Cu²⁺,Ni²⁺ and Zn²⁺ ions, the first linker groups (L¹) are selected from4,4′-bipyridylacetylene, 4,4′-bipyridine and pyrazine and the secondliker groups (L²) are selected from SiF₆ ²⁻, TiF₆ ²⁻, SnF₆ ²⁻, ZrF₆ ²⁻and GeF₆ ²⁻.

Preferably the metal species (M) are selected from Cu²⁺, Ni²⁺ and Zn²⁺ions, the first linker groups (L¹) are selected from4,4′-bipyridylacetylene, 4,4′-bipyridine and pyrazine and the secondliker groups (L²) are selected from SiF6²⁻, TiF₆ ²⁻ and SnF₆ ²⁻ ions.

Suitably the metal species (M) are Cu²⁺ ions, the first linker groups(L¹) are selected from 4,4′-bipyridylacetylene and 4,4′-bipyridine andthe second liker groups (L²) are TiF₆ ²⁻ ions.

The first sorbent material may be prepared by any suitable method, forexample by solid state synthesis, crystallisation from a suitablesolvent, direct mixing, slurrying or mechanochemistry, each with orwithout heating. For example, the hybrid porous material may be preparedby any of the above methods by reacting an approximately equimolaramount of the metal species (M), for example a salt of the metal species(M), the first linker group (L¹), for example a two-connected nitrogenligand, and the second linker group (L²), for example a salt of anAX_(n) ^(Y−) anion, optionally together in a suitable solvent, forexample a mixture of water and methanol, optionally with heating.

In some embodiments, the three-dimensional lattice of metal species (M)and linker groups (L¹ and L²) may be interpenetrated. By interpenetratedwe mean that two or more three-dimensional lattices of metal species (M)and linker groups are interlocked so that they cannot be separatedwithout breaking chemical bonds, for example as shown in structure (III)wherein the first three-dimensional lattice comprises M, L¹ and L² andthe second three-dimensional lattice comprises M′, L¹′ and L²′:

Whether a hybrid porous material forming reaction, such as thosedescribed above, forms an interpenetrated hybrid porous material or anon-interpenetrated hybrid porous material may depend on the particularreaction type and/or the solvent used (if any) and/or the temperature ofthe reaction and/or the concentration of the reaction mixture, asdescribed in “Temperature and Concentration Control overInterpenetration in a Metal-Organic Material” (Zaworotko, M. J. et al,J. Am. Chem. Soc., 2009, 131, 17040-17041) and “Template-directedsynthesis of metal-organic materials” (Zaworotko, M. J. and Zhang, Z.,Chem. Soc. Rev., 2014, 43, 5444).

The three-dimensional lattice of metal species (M) and linker groups,which provides the hybrid porous material used in the method of thisfirst aspect, comprises pores. The pores are formed in the sections ofthe three-dimensional lattice defined by M, L¹ and L². Therefore in themethod, acetylene may pass through openings of the pores in the hybridporous material defined by M, L¹ and L² and become bound to thethree-dimensional lattice within said pores. It is believed that thesize of said pores may contribute to the selectivity and capacityexhibited by the hybrid porous materials of the present invention.

Suitably the hybrid porous material comprises pores with an effectivepore size of from 3.5 to 12 Å.

Effective pore size may be additionally or alternatively defined as theeffective pore diameter. Effective pore size/diameter is a measure ofthe dimensions of the pore at the narrowest point of the pore. Thesevalues take into account the van der Waals radii of the atoms lining thepore wall (i.e. they are not atom to atom distances).

In alternative embodiments the first linker groups (L¹) are inorganiclinkers and are as defined above in relation to the second linker groups(L²), and the second linker groups (L²) are organic linkers and are asdefined above in relation to the first linker groups (L¹). In otherwords, in the hybrid porous material used in the method of the firstaspect, the above definitions of the first linker groups (L¹) and thesecond linker groups (L²) may be interchanged.

The first sorbent material is selected according to the abovedescription in order to have selectivity for acetylene over ethylene,and suitably over ethane and carbon dioxide. Suitably the metal species(M) are Cu²⁺ ions, the first linker groups (L¹) are4,4′-bipyridylacetylene, the second liker groups (L²) are TiF₆ ²⁻ ionsand the three-dimensional lattice of metal species (M) and linker groupsis interpenetrated. This particular hybrid porous material may be knownas TIFSIX-2-Cu-i.

In some embodiments, the first sorbent material has the chemicalformula: M_(x)(L¹)₂(L²)Y_(z) wherein the metal species (M) is selectedfrom atoms or ions of Co, Cu, Zn and Ni, wherein x is an integer from 1to 3, L¹ is a two-connected nitrogen ligand as defined above, L² is adicarboxylic acid, Y is an anion and z is an integer from 0 to 3.Suitably L² is a C₂₋₁₀ dicarboxylic acid. Suitably L² is selected fromchiral or racemic tartaric acid, malic acid, succinic acid, fumaricacid, 2,3-dibromosuccinic acid, aspartic acid, 1,4-benzenedicarboxylicacid and 1,3-benzenedicarboxylic acid.

Suitably the metal species (M) are Co²⁺ or Ni²⁺ ions, suitably Ni²⁺ions, the first linker groups (L¹) are 4,4′-bipyridine and the secondlinker groups (L²) are tartaric acid ions, suitably L-tartaric acidions. In addition, halide anions are bridging the metal species. Thisparticular hybrid porous material may be known as [Ni₂(bpy)₂(L-tart)F₂].

In such embodiments, the first sorbent material may be[Ni₂(bpy)₂(L-tart)F₂].

The Second Sorbent Material

The second sorbent material is suitably a porous material which has ahigher adsorption selectivity for ethane than for ethylene and/oracetylene, and suitably carbon dioxide.

Suitably the second sorbent material is an ultramicroporous materialwhich has a higher adsorption selectivity for ethane than for ethyleneand acetylene, and suitably also for carbon dioxide.

Suitably the second sorbent material is an ultramicroporous materialcomprising pores which are hydrophobic or weakly hydrophilic. Suitablythe pores of the second sorbent material are more hydrophobic than thepores of the first sorbent material, and any third or further sorbentmaterial present. Such a hydrophobic pore nature suitably providesadsorption selectivity for ethane over ethylene, acetylene and suitablycarbon dioxide. The inventors have found that such hydrophobic pores mayprovide only weak van der Waals or hydrogen bond interactions which maytherefore preferentially bind to relatively non-polar molecules such asethane.

Suitably the pores of the second sorbent have an average size of lessthan 0.7 nm, for example of less than 0.6 nm or less than 0.5 nm.

Suitably the second sorbent material has the chemical formula:M₂(L¹)₂(L²). Suitably the second sorbent material is formed by metalions, carboxylate ligands and azolate ligands, appropriately selected inorder to provide selectivity for ethane over ethylene, and suitably overacetylene and carbon dioxide. Suitable azolate ligands includeimidazolate and triazolate ligands.

Suitably the second sorbent material is a Zn-based framework material,suitably of formula Zn₂(A)₂(B).

A is suitably selected from amino-substituted heterocyclic ligandscomprising at least two donor atoms which are nitrogen atoms. Suitablythe at least two nitrogen atoms each comprise a lone pair of electronssuitable for binding to a metal species. A is suitably selected fromamino-substituted heterocyclic ligands comprising at least three donoratoms which are nitrogen atoms. Suitably A is an ionic compound.Suitably A is a triazolate ion.

Suitably A is an ion derived from 3-amino-1,2,4-triazole (Hatz, formula(III)), an ion derived from 3,5-diamino-1,2,4-triazole (Hdatz, formula(IV)) or an ion derived from 1,2,4-triazole (V).

B is suitably selected from dicarboxylate ligands. Suitably B is adicarboxylate ligand comprising at least one phenyl group. Suitably B isan ion derived from isophthalic acid (H₂ipa, formula (VI)) or4,4′-oxobisbenzoic acid (H₂oba, formula (VII)).

Compound (VI) may be optionally substituted at the 5-position. Forexample, the X group may be selected from C₁-C₄ alkyl, C₁-C₄ alkoxy,C₁-C₄ alkylamino, C₁-C₄ alkylthio, hydroxy, amino, nitro, thiol, bromo,chloro, fluoro, CF₃, CHF₂ or CH₂F groups. Suitably X is selected from H,NH₂, NO₂, F, Cl, Br, methyl or ethyl.

Suitably A is an ion derived from 3-amino-1,2,4-triazole and B is an ionderived from isophthalic acid. Therefore the second sorbent material issuitably Zn₂(atz)₂(ipa). This material may be referred to as Zn-atz-ipa.This material is as described in Kai-Ji Chen et al in “NewZn-Aminotriazolate-Dicarboxylate Frameworks: Synthesis, Structures andAdsorption Properties”, Cryst. Growth Des., 2013, 13, 2118-2123.

In some embodiments, the second sorbent material is suitably anultramicroporous material of formula M(L¹)₂(L²) as defined above for thefirst sorbent material, which may additionally comprise anions such ashalogen ions, where appropriate. Therefore the first sorbent may havethe formula M_(x)(L¹)₂(L²)Y_(z), wherein M is a transition metal cation,wherein x is an integer from 1 to 3, suitably 1 or 2, Y is an anion,suitably a halogen anion, and z is an integer from 0 to 3, suitably 1 or2. Suitably the second sorbent material is an ultramicroporous materialof formula M₂(L¹)₂(L²)Y₂, wherein Y is a halogen anion, suitably F⁻,suitably wherein M is Co²⁺ or Ni²⁺ and L¹ is as described in relation tothe first sorbent material. Suitably L² is a di-carboxylic acid asdefined above in relation to linker B of Zn₂(A)₂(B), or a di-carboxylicacid equivalent linker with an azolate group, for example tetrazolate,triazolate, pyrazolate, imidazolate, such as Tzba which is derived from4-(1H-tetrazol-5-yl)benzoic acid (structure VIII below).

In such embodiments, the second sorbent material may be[Co₂(bpy)₂(Tzba)F₂].

Suitably the first sorbent material is TIFSIX-2-Cu-i and the secondsorbent material is Zn-atz-ipa. Therefore the first aspect of thepresent invention may provide a method of obtaining a target gas, suchas ethylene or methane, from a gaseous composition comprising the targetgas, acetylene and ethane, the method comprising the step of contactingthe gaseous composition with a sorbent media to remove at least some ofthe acetylene and at least some of the ethane from the gaseouscomposition; wherein the sorbent media comprises TIFSIX-2-Cu-i andZn-atz-ipa; wherein the TIFSIX-2-Cu-i selectively adsorbs the acetyleneover the target gas and the ethane; and wherein the Zn-atz-ipaselectively adsorbs the ethane over the target gas and the acetylene.

Additionally or alternatively, the first sorbent material may be[Ni₂(bpy)₂(L-tart)F₂] and/or the second sorbent material may be[Co₂(bpy)₂(Tzba)F₂], to carry out the method described herein. Thereforein some embodiments, the first sorbent material may be selected fromTIFSIX-2-Cu-i and [Ni₂(bpy)₂(L-tart)F₂], and the second sorbent materialmay be selected from Zn-atz-ipa and [Co₂(bpy)₂(Tzba)F₂]. In thefollowing description, [Ni₂(bpy)₂(L-tart)F₂] may replace TIFSIX-2-Cu-iand/or [Co₂(bpy)₂(Tzba)F₂] may replace Zn-atz-ipa.

It is believed that in TIFSIX-2-Cu-i, C₂H₂, C₂H₄ and C₂H₆ moleculeslocalize so that every molecule can interact with two TiF₆ ²⁻ anionsthrough C—HF interactions. However, C₂H₂ has shorter contacts withdistances of 2.46 and 2.50 Å compared to C₂H₄ (2.45 and 2.52 Å) and C₂H₆(2.62 and 2.90Å). Moreover, the more acidic C₂H₂ molecule (pKa=26, vsC₂H₄, pKa=45, and C₂H₆, pKa=62) may form stronger hydrogen bondinginteractions. For TIFSIX-2-Cu-i, CO₂ molecules interact with two F atomsfrom one TiF₆ ²⁻ anion, with short interaction distances between the Catom of CO₂ and F atoms of TiF₆ ²⁻ anion (2.65 and 3.48 Å). It istherefore thought that the interaction strengths in TIFSIX-2-Cu-i isC₂H₂>CO₂>C₂H₄>C₂H₆.

The inventors have also unexpectedly found that Zn-atz-ipa and[Co₂(bpy)₂(Tzba)F₂] selectively adsorbs ethane. Without being bound bytheory, it is thought that the all six hydrogen atoms present in onemolecule of ethane interact with the pore surface of Zn-atz-ipa, givingrise to a tight-fitting binding site. Smaller molecules such as carbondioxide and ethylene do not have as many contact points and so thebinding site does not fit as closely. As such these small molecules arenot as tightly bound. The strength of interactions in Zn-atz-ipa thusfollows the sequence C₂H₆>C₂H₄>C₂H₂>CO₂. Likewise, [Co₂(bpy)₂(Tzba)F₂]selectively adsorbs C₂H₆ over C₂H₄ and CO₂.

In such embodiments the sorbent media may comprise TIFSIX-2-Cu-i andZn-atz-ipa in a weight ratio of from 1:1 to 1:20 TIFSIX-2-Cu-i toZn-atz-ipa, suitably of from 1:5 to 1:15, for example a weight ratio ofapproximately 1:10 TIFSIX-2-Cu-i to Zn-atz-ipa.

In alternative embodiments, the second sorbent material may have theformula M(C₂N₃H₂)₂ wherein M is selected from Mg, Mn, Fe, Co, Cu or Zn.Suitably the second sorbent material is formed by metal ions andtriazole, suitably 1H-1,2,3-triazole, appropriately selected in order toprovide selectivity for ethane over ethylene, and suitably overacetylene and carbon dioxide. These materials may be referred to as METframework materials. These materials are as described in Felipe Gándaraet al in “Porous, Conductive Metal-Triazolates and Their StructuralElucidation by the Charge-Flipping Method”, Chem. Eur. J., 2012, 18,10595-10601.

Suitably the second sorbent material has the formula Mn(C₂N₃H₂)₂,wherein the ligand is 1H-1,2,3-triazole. This material may be referredto as MET-2.

Suitably the second sorbent material has the formula Cu(C₂N₃H₂)₂,wherein the ligand is 1H-1,2,3-triazole. This material may be referredto as MET-5.

Suitably the second sorbent material has the formula Zn(C₂N₃H₂)₂,wherein the ligand is 1H-1,2,3-triazole. This material may be referredto as MET-6.

Suitably the first sorbent material is TIFSIX-2-Cu-i and the secondsorbent material is a MET framework material, suitably selected fromMET-2, MET-5 and MET-6. Therefore the first aspect of the presentinvention may provide a method of obtaining a target gas, such asethylene or methane, from a gaseous composition comprising the targetgas, acetylene and ethane, the method comprising the step of contactingthe gaseous composition with a sorbent media to remove at least some ofthe acetylene and at least some of the ethane from the gaseouscomposition; wherein the sorbent media comprises TIFSIX-2-Cu-i and a METframework material; wherein the TIFSIX-2-Cu-i selectively adsorbs theacetylene over the target gas and the ethane; and wherein the METframework material selectively adsorbs the ethane over the target gasand the acetylene.

In such embodiments the sorbent media may comprise TIFSIX-2-Cu-i and aMET framework material in a weight ratio of from 1:1 to 1:20TIFSIX-2-Cu-i to the MET framework material, suitably of from 1:5 to1:15, for example a weight ratio of approximately 1:10 TIFSIX-2-Cu-i tothe MET framework material.

The Third Sorbent Material

In some embodiments, the gaseous composition comprises a third gas,suitably carbon dioxide. In such embodiments, the gaseous mixturesuitably comprises, consists essentially of or consists of the targetgas, acetylene, ethane and carbon dioxide. In such embodiments, thesorbent media comprises the first and second sorbent materials asdescribed above and a third sorbent material, wherein the third sorbentmaterial has a higher adsorption selectivity for the third gas than forthe target gas. Suitably the third sorbent material has a higheradsorption selectivity for the third gas than for target gas, the firstgas and the second gas. The third gas is suitably carbon dioxide andtherefore the third sorbent material suitably has a higher adsorptionselectivity for carbon dioxide than for the target gas, suitablyethylene or methane. The third sorbent material suitably has a higheradsorption selectivity for carbon dioxide than for the target gas andacetylene. The third sorbent material suitably has a higher adsorptionselectivity for carbon dioxide than for the target gas, acetylene andethane. The third sorbent is different to the first and second sorbents.

The third sorbent material is suitably an ultramicroporous material asdefined above wherein one of L¹ and L² is an organic linker group andthe other of L¹ and L² is an inorganic linker group, which has a higheradsorption selectivity for carbon dioxide than for the target gas,acetylene and ethane. The third sorbent material may be appropriatelyselected from the ultramicroporous materials described in relation tothe first sorbent material.

Suitably the third sorbent material has the chemical formula:M(L¹)₂(L²). Suitably the metal species (M) are transition metal atoms orions. Suitably the metal species (M) are Ni²⁺ ions. Suitably the firstlinker groups (L¹) are pyrazine. Suitably the second linker groups (L²)are SiF₆ ²⁻ ions.

In the third sorbent material, the metal species (M) are Ni²⁺ ions, thefirst linker groups (L¹) are pyrazine, the second liker groups (L²) areSiF₆ ²⁻ ions and the three-dimensional lattice of metal species (M) andlinker groups is not interpenetrated. This particular hybrid porousmaterial may be known as SIFSIX-3-Ni.

In some embodiments, the first sorbent material is TIFSIX-2-Cu-i, thesecond sorbent material is Zn-atz-ipa and the third sorbent material isSIFSIX-3-Ni. Therefore the first aspect of the present invention mayprovide a method of obtaining a target gas, for example ethylene ormethane, from a gaseous composition comprising the target gas,acetylene, ethane and carbon dioxide, the method comprising the step ofcontacting the gaseous composition with a sorbent media to remove atleast some of the acetylene, at least some of the ethane and at leastsome of the carbon dioxide from the gaseous composition; wherein thesorbent media comprises TIFSIX-2-Cu-i, Zn-atz-ipa and SIFSIX-3-Ni;wherein the TIFSIX-2-Cu-i selectively adsorbs the acetylene over thetarget gas, ethane and carbon dioxide; wherein the Zn-atz-ipaselectively adsorbs the ethane over the taget gas, acetylene and carbondioxide; and wherein the SIFSIX-3-Ni selectively adsorbs the carbondioxide over the target gas, acetylene and ethane. Suitably the methodremoves substantially all of the acetylene, ethane and carbon dioxidefrom the gaseous composition to provide the target gas in high purity,for example a purity of at least 95 wt %, suitably at least 99 wt %,suitably at least 99.9 wt %, suitably at least 99.99 wt %.

It is thought that in SIFSIX-3-Ni, CO₂ binding is driven by interactionswith four electronegative F atoms from four independent SiF₆ ²⁻ anions.C₂H₂ is trapped through multiple C—HF interactions with HF distances of3.3-4.5 A between C₂H₂ and eight SiF₆ ²⁻ anions. In contrast, C₂H₄ andC₂H₆ exhibit simultaneous interactions with two and six SiF₆ ²⁻ anions,respectively. Though there are fewer contacts with anions, shorterinteraction distances of 2.51 and 2.62 Åfor C₂H₄ suggest that theadsorption energy of C₂H₄ will be favourable vs. C₂H₆(2.59-2.76 Å). ThusSIFSIX-3-Ni preferentially adsorbs CO₂>C₂H₂>C₂H₄>C₂H₆.

In such embodiments the sorbent media may comprise a weight ratio ofTIFSIX-2-Cu-i to SIFSIX-3-Ni of from 2:1 to 1:2, suitably from 1.5:1 to1:1.5, suitably approximately 1:1.25. The sorbent media may compriseTIFSIX-2-Cu-i, Zn-atz-ipa and SIFSIX-3-Ni in a weight ratio ofapproximately 1/1.25/10, suitable for use with an industrial gasmixture.

In alternative embodiments, the first sorbent material is TIFSIX-2-Cu-i,the second sorbent material is a MET framework material and the thirdsorbent material is SIFSIX-3-Ni. Therefore the first aspect of thepresent invention may provide a method of obtaining a target gas, forexample ethylene or methane, from a gaseous composition comprising thetarget gas, acetylene, ethane and carbon dioxide, the method comprisingthe step of contacting the gaseous composition with a sorbent media toremove at least some of the acetylene and at least some of the ethanefrom the gaseous composition; wherein the sorbent media comprisesTIFSIX-2-Cu-i, a MET framework material and SIFSIX-3-Ni; wherein theTIFSIX-2-Cu-i selectively adsorbs the acetylene over the target gas,ethane and carbon dioxide; wherein the MET framework materialselectively adsorbs the ethane over the target gas, acetylene and carbondioxide; and wherein the SIFSIX-3-Ni selectively adsorbs the carbondioxide over the target gas, acetylene and ethane.

In such embodiments the sorbent media may comprise a weight ratio ofTIFSIX-2-Cu-i to SIFSIX-3-Ni of from 2:1 to 1:2, suitably from 1.5:1 to1:1.5, suitably approximately 1:1.25. The sorbent media may compriseTIFSIX-2-Cu-i, a MET framework material and SIFSIX-3-Ni a weight ratioof approximately 1/1.25/10.

The inventors have found that these combinations of first, second andthird sorbent materials can provide the target gas, such as ethylene ormethane, in high purity from a gaseous composition comprising the targetgas, acetylene, ethane and carbon dioxide.

The contacting of the gaseous composition with the sorbent media may becarried out at any suitable temperature below 120° C., suitably at atemperature of from −20° C. to 60° C., suitably of from 0° C. to 50° C.,suitably from 0° C. to 40° C., suitably from 10° C. to 40° C. Thecontacting of the gaseous composition with the sorbent media may becarried out at ambient temperature. Such a temperature may also bereferred to as room temperature. The temperature of this step may bechosen according to the selectivity profile of the first, second andthird (if present) sorbent materials for the first, second or third gas(if present) respectively at different temperatures of said gases.

The method being able to function effectively at ambient temperature mayprovide cost and/or energy savings and may therefore provide asignificant advantage over methods of the prior art.

The contacting of the gaseous composition with the sorbent media may becarried out at a pressure of from 0.1 to 5 bar, suitably from 0.4 to 2bar, for example from 0.5 bar to 1.5 bar or approximately 1 bar.Suitably the contacting of the gaseous composition with the sorbentmedia is carried out at a pressure of 1 bar. The pressure of this stepmay be chosen according to the selectivity profile of the first, secondand third (if present) sorbent materials for the first, second or thirdgas (if present) respectively at different pressures of said gases.

In embodiments wherein the gaseous composition comprises acetylene,ethylene, ethane and carbon dioxide, the partial pressures of thesegases are suitably acetylene 1%, ethylene 33%, ethane 33% and carbondioxide 33%, of the total pressure of the gaseous composition. Thereforethe partial pressures of the different gases are suitably acetylene 0.01bar, ethylene 0.33 bar, ethane 0.33 bar and carbon dioxide 0.33 bar,wherein the gaseous mixture has a pressure of approximately 1 bar.

Suitably the method of this first aspect is carried out under ambientpressure. The method being able to function effectively at ambientpressure may lead to significant cost and/or energy savings and mayavoid the use of complex equipment, which may be advantageous over somemethods of the prior art.

The method of the first aspect suitably provides the target gas, such asethylene or methane in a higher purity than some methods of the priorart. Suitably the present invention provides the target gas with apurity of at least 95 wt %, suitably at least 99 wt %, suitably at least99.9 wt %, suitably at least 99.99 wt %.

The method of the first aspect suitably provides ethylene in a highpurity suitable for polymer manufacture, suitably in a higher puritythan some methods of the prior art. Suitably the present inventionprovides ethylene with a purity of at least 95 wt %, suitably at least99 wt %, suitably at least 99.9 wt %, suitably at least 99.99 wt %.

The method of the first aspect involves obtaining a target gas from agaseous composition comprising the target gas, a first gas and a secondgas, the method comprising the step of contacting the gaseouscomposition with a sorbent media. Therefore the method of the firstaspect may be considered to involve the steps of:

a) providing a gaseous composition comprising a target gas, a first gasand a second gas;

b) contacting the gaseous composition with a sorbent media comprising afirst sorbent material and a second sorbent material, to remove at leastsome of the first gas and at least some of the second gas from thegaseous composition; wherein the first sorbent material has a higheradsorption selectivity for the first gas than for the target gas and thesecond sorbent material has a higher adsorption selectivity for thesecond gas than for the target gas; and

c) collecting the target gas from the sorbent media.

Suitably the steps of the method are carried out in the order step a)followed by step b) followed by step c).

Suitably the target gas is ethylene or methane.

In some embodiments, the target gas is ethylene. Suitably the method ofthe first aspect involves obtaining ethylene from a gaseous compositioncomprising ethylene, a first gas and a second gas, the method comprisingthe step of contacting the gaseous composition with a sorbent media.

Therefore the method of the first aspect may be considered to involvethe steps of:

a) providing a gaseous composition comprising ethylene, a first gas anda second gas;

b) contacting the gaseous composition with a sorbent media comprising afirst sorbent material and a second sorbent material, to remove at leastsome of the first gas and at least some of the second gas from thegaseous composition; wherein the first sorbent material has a higheradsorption selectivity for the first gas than for ethylene and thesecond sorbent material has a higher adsorption selectivity for thesecond gas than for ethylene; and

c) collecting ethylene from the sorbent media.

The method may be a continuous process whereby the gaseous mixture isdirected into contact with the sorbent media in a suitable vessel andethylene is collected from the sorbent media once the first and secondgases have been adsorbed by the sorbent media.

The method may involve, after step c), a step d) of removing the firstgas and the second gas from the sorbent media. This may be considered tobe a regeneration of the sorbent media. Suitably the sorbent media canbe regenerated after each use, to be used again in the method of thefirst aspect, for example in a second or further sequence of steps a) toc). Regenerating the sorbent media suitably involves removing the firstand second gases, and any third or further gases if present, from thesorbent media onto or into which these gases have been adsorbed duringstep b). This may be achieved by heating for sorbent media and/orflowing a diluent gas through the sorbent media. For example, thesorbent material may be regenerated at a temperature of 60° C. under Heflow. Suitably the regeneration takes place for up to 2 hours, forexample up to 1 hour. Suitably the regeneration takes less than 10minutes. Suitably the regeneration takes place until the acetylenehydrocarbon and CO₂ signal in a mass spectrum of effluent gas hasdisappeared.

Therefore the method may involve, after step d), repeating steps a) toc). Suitably the sorbent material may be used more than once in a repeatof steps a) to c). Suitably the sorbent material may be used at leasttwice or three times with no or minimal loss in adsorption performance.Suitably the sorbent material may be used at least 10 times with no orminimal loss in adsorption performance. Suitably the sorbent materialmay be used 50 times with no or minimal loss in adsorption performance.Suitably the sorbent material may be used more than 50 times whilststill providing sufficient adsorption performance to purify the targetgas to the levels of purity discussed above.

According to a third aspect of the present invention, there is provideda method of removing ethane from a gaseous composition, the methodcomprising the step of contacting the gaseous composition with a sorbentmaterial to remove at least some of the ethane, wherein the sorbentmaterial comprises an ultramicroporous material of formula Zn₂(A)₂(B);wherein A is an amino-substituted heterocyclic ligand and B is adicarboxylate ligand. Therefore the sorbent material suitably isZn₂(atz)₂(ipa).

The method, gaseous composition and sorbent material of this thirdaspect may have any of the suitable features and advantages described inrelation to the first aspect.

The method, gaseous composition and sorbent material of this thirdaspect may have any of the suitable features and advantages described inrelation to the first aspect.

Suitably the pores of the sorbent material are hydrophobic or weaklyhydrophilic. The sorbent material may have any of the suitable featuresor advantages of the second sorbent material described in relation tothe first and second aspects of the present invention.

The gaseous composition suitably comprises ethylene and ethane, suitablyethylene, ethane and acetylene, suitably ethylene, ethane, acetylene andcarbon dioxide. The gaseous composition may have any of the suitablefeatures or advantages of the gaseous composition described in relationto the first and second aspects of the present invention.

In some embodiments, the gaseous composition comprises methane andethane, suitably methane, ethane and acetylene, suitably methane,ethane, acetylene and carbon dioxide.

The method of removing ethane from a gaseous composition of this thirdaspect may have any of the suitable features or advantages of the methodof obtaining ethylene from a gaseous composition comprising ethylene, afirst gas and a second gas, of the first aspect of the presentinvention.

According to a fourth aspect of the present invention, there is provideda use of an ultramicroporous material of formula Zn₂(A)₂(B); wherein Ais an amino-substituted heterocyclic ligand and B is a dicarboxylateligand, to separate ethane from a gas mixture comprising ethane.

The use of this fourth aspect may have any of the features andadvantages described in relation to the third aspect, and therefore thefirst and second aspects.

According to a fifth aspect of the present invention, there is provideda method of removing ethane from a gaseous composition, the methodcomprising the step of contacting the gaseous composition with a sorbentmaterial to remove at least some of the ethane, wherein the sorbentmaterial comprises an ultramicroporous material of formulaM_(x)(L¹)₂(L²)Y_(z) wherein M is Co²⁺ or Ni²⁺ , wherein x is an integerfrom 1 to 3, L¹ is an organic linker group, L² is a di-carboxylic acidlinker or a di-carboxylic acid equivalent linker having an azolategroup, Y is an inorganic anion and z is an integer from 0 to 3.

The method, gaseous composition and sorbent material of this fifthaspect may have any of the suitable features and advantages described inrelation to the first aspect.

Suitably the ultramicroporous material is [Co₂(bpy)₂(Tzba)F₂].

Suitably the pores of the sorbent material are hydrophobic or weaklyhydrophilic. The sorbent material may have any of the suitable featuresor advantages of the second sorbent material described in relation tothe first and second aspects of the present invention.

The gaseous composition suitably comprises ethylene and ethane, suitablyethylene, ethane and acetylene, suitably ethylene, ethane, acetylene andcarbon dioxide. The gaseous composition may have any of the suitablefeatures or advantages of the gaseous composition described in relationto the first and second aspects of the present invention.

In some embodiments, the gaseous composition comprises methane andethane, suitably methane, ethane and acetylene, suitably methane,ethane, acetylene and carbon dioxide.

The method of removing ethane from a gaseous composition of this fifthaspect may have any of the suitable features or advantages of the methodof obtaining ethylene from a gaseous composition comprising ethylene, afirst gas and a second gas, of the first aspect of the presentinvention.

According to a sixth aspect of the present invention, there is provideda use of an ultramicroporous material of formula M_(x)(L¹)₂(L²)Y_(z)wherein M is Co²⁺ or Ni²⁺, wherein x is an integer from 1 to 3, L¹ is anorganic linker group, L² is a di-carboxylic acid linker or adi-carboxylic acid equivalent linker having an azolate group, Y is aninorganic anion and z is an integer from 0 to 3, to separate ethane froma gas mixture comprising ethane.

The use of this sixth aspect may have any of the features and advantagesdescribed in relation to the fifth aspect, and therefore the first andsecond aspects.

According to a seventh aspect of the present invention, there isprovided a method of removing acetylene from a gaseous composition, themethod comprising the step of contacting the gaseous composition with asorbent material to remove at least some of the acetylene, wherein thesorbent material comprises an ultramicroporous material of formula:M_(x)(L¹)₂(L²)Y_(z) wherein the metal species (M) is selected from atomsor ions of Co, Cu, Zn and Ni, wherein x is an integer from 1 to 3, L¹ isa two-connected nitrogen ligand as defined above, L² is a dicarboxylicacid, Y is an anion and z is an integer from 0 to 3. Suitably L² is aC₂₋₁₀ dicarboxylic acid. Suitably L² is selected from chiral or racemictartaric acid, malic acid, succinic acid, fumaric acid,2,3-dibromosuccinic acid, aspartic acid, 1,4-benzenedicarboxylic acidand 1,3-benzenedicarboxylic acid.

The method, gaseous composition and sorbent material of this seventhaspect may have any of the suitable features and advantages described inrelation to the first aspect.

Suitably the sorbent material comprises [Ni₂(bpy)₂(L-tart)F₂]. Suitablythe sorbent material is [Ni₂(bpy)₂(L-tart)F₂].

The gaseous composition suitably comprises ethylene and acetylene,suitably ethylene, ethane and acetylene, suitably ethylene, ethane,acetylene and carbon dioxide. The gaseous composition may have any ofthe suitable features or advantages of the gaseous composition describedin relation to the first and second aspects of the present invention.

In some embodiments, the gaseous composition comprises methane, ethaneand acetylene, suitably methane, ethane, acetylene and carbon dioxide.

The method of removing acetylene from a gaseous composition of thisseventh aspect may have any of the suitable features or advantages ofthe method of obtaining ethylene from a gaseous composition comprisingethylene, a first gas and a second gas, wherein the first gas isacetylene, of the first aspect of the present invention.

According to an eighth aspect of the present invention, there isprovided a use of an ultramicroporous material of formulaM_(x)(L¹)₂(L²)Y_(z) to separate ethane from a gas mixture comprisingethane, wherein the metal species (M) is selected from atoms or ions ofCo, Cu, Zn and Ni, wherein x is an integer from 1 to 3, L¹ is atwo-connected nitrogen ligand as defined above, L² a dicarboxylic acid,Y is an anion and z is an integer from 0 to 3. Suitably L² is a C₂₋₁₀dicarboxylic acid. Suitably L² is selected from chiral or racemictartaric acid, malic acid, succinic acid, fumaric acid,2,3-dibromosuccinic acid, aspartic acid, 1,4-benzenedicarboxylic acidand 1,3-benzenedicarboxylic acid.

The use of this eighth aspect may have any of the features andadvantages described in relation to the seventh aspect, and thereforethe first and second aspects.

Suitably the sorbent material comprises [Ni₂(bpy)₂(L-tart)F₂]. Suitablythe sorbent material is [Ni₂(bpy)₂(L-tart)F₂].

According to a ninth aspect of the present invention, there is provideda sorbent media comprising a first sorbent material and a second sorbentmaterial; wherein the first sorbent material has a higher adsorptionselectivity for a first gas than for a target gas; wherein the secondsorbent material has a higher adsorption selectivity for a second gasthan for the target gas; and wherein the first sorbent material and thesecond sorbent material are different ultramicroporous materials.

The gaseous composition and sorbent media may have any of the suitablefeatures and advantages described in relation to the first and secondaspects.

According to a tenth aspect of the present invention, there is providedan apparatus for obtaining a target gas from a gaseous compositioncomprising the target gas, a first gas and a second gas, the apparatuscomprising a sorbent media according to the ninth aspect.

The sorbent media is suitably arranged on the support in a configurationto ensure maximum adsorption. Suitably the apparatus comprises means fordirecting the gaseous composition through or across the sorbentmaterial.

In some embodiments the device may be electrically powered. Suitably theapparatus is powered by renewable resources.

In some embodiments the target gas provided by the method, use orapparatus described herein may undergo further treatment. In alternativeembodiments the target gas provided by the method, use or apparatusdescribed herein may be used directly in a subsequent process.

For example, wherein the target gas is ethylene, the ethylene may beused directly in the production of poly(ethylene) and other relatedpolymers.

In the methods of the present invention, if water vapour is present inthe gaseous mixture then a desiccant material may be used to remove saidwater vapour. The gaseous mixture may be contacted with a desiccantmaterial before or after contacting the sorbent media.

According to an eleventh aspect of the present invention, there isprovided an ultramicroporous material of formula [Co₂(bpy)₂(Tzba)F₂].

According to a twelfth aspect of the present invention, there isprovided a sorbent media comprising [Co₂(bpy)₂(Tzba)F₂].

The sorbent media may have any of the suitable features and advantagesdescribed herein, particularly with reference to the sorbent media ofthe ninth aspect.

The invention will now be further described by reference to theaccompanying figures and examples.

Examples

In the following examples, the following materials were used:

Materials

Ammonium hexafluorotitanate((NH₄)₂TiF₆, 99.99%, Sigma-Aldrich), ammoniumhexafluorosilicate ((NH₄)₂SiF₆, 99.999%, Sigma-Aldrich), copper (II)tetrafluoroborate hydrate (Cu(BF₄)₂.xH₂O, Sigma-Aldrich), zinc nitratehexahydrate (Zn(NO₃)₂.6H₂O, 98%, Sigma-Aldrich), nickel(II) nitratehexahydrate (Ni(NO₃)₂.6H₂O, Sigma-Aldrich), isophthalic acid (C₈H₆O₄,99%, TCI), 3-amino-1,2,4-triazole (C₂H₄N₄, 98%, TCI), pyrazine (C₄H₄N₂,99%, Sigma-Aldrich) and solvents (DMF and methanol, HPLC grade of 99.9%)from Sigma-Aldrich were purchased and directly used.

He (99.999%), CO₂ (99.999%), N₂ (99.9995%), C₂H₂ (98.5%), C₂H₄ (99.92%)and C₂H₆ (99%) were purchased from BOC gases Ireland.

Methods

Synthesis of TIFSIX-2-Cu-i

This material was synthesized according to the method described in K.-J.Chen et al., Chem 1, 753-765 (2016).

An aqueous solution (60 mL) obtained from dissolving 2.4 g ofCu(BF₄)₂.xH₂O and 2.0 g of (NH₄)₂TiF₆ was added into a methanol solution(60 mL) dissolving 2.07 g of 4,4′-bipyridylacetylene. This mixture wastransferred to a 200 mL borosilicate bottle, and then heated at 80° C.for 24 hours. After heating, the mixture was filtrated and thelight-green powder was harvested. The powder was exchanged with freshmethanol twice a day for three days. Yield: 65% based on ligand.

Synthesis of Zn-atz-ipa

This material was synthesized based on the method described in K.-J.Chen et al., Cryst. Growth Des. 13, 2118-2123 (2013).

Mixing of Zn(NO₃)₂.6H₂O (20mmol, 5.96 g), H₂ipa (10mmol, 1.66 g), Hatz(20 mmol, 1.68 g) in a solvent mixture of DMF (60 mL), MeOH (60 mL), andH₂O (30 mL) afforded a suspension solution, followed by three minutes ofsonication. Then this mixture was capped in a 250 mL borosilicate bottleand heated at 130° C. for 72 hours, which was followed by slow coolingprocess to room temperature with 10° C./hour. After cooling, the motherliquor was decanted and the colorless crystalline product can beharvested by filtration. The white sample was rinsed three times withfresh DMF of 20 mL and dried in air. Yield: 55% based on metal salt.

Synthesis of Zn-datz-ipa

This material was synthesized based on the method described in K.-J.Chen et al., Cryst. Growth Des. 13, 2118-2123 (2013).

Synthesis of MET-2, MET-5 and MET-6

These materials were synthesized based on the method describe in FelipeGándara et al in “Porous, Conductive Metal-Triazolates and TheirStructural Elucidation by the Charge-Flipping Method”, Chem. Eur. J.,2012, 18, 10595-10601.

Synthesis of SIFSIX-3-Ni

This material was synthesized using the method described in A. Kumar etal., Angew. Chem. Int. Ed. 54, 14372-14377 (2015).

By keeping stirring a slurry mixture of 437 mg (1.5 mmol) ofNi(NO₃)₂.6H₂O, 269 mg (1.5 mmol) of (NH₄)₂SiF₆ and 240 mg (3 mmol) ofpyrazine in 3 mL of water for 3 days, a microcrystalline powder inpurple was harvested. The suspension mixture was filtered and purplepowder was then soaked in methanol for one day, followed by two morewashing by 10 ml methanol. After this, SIFSIX-3-Ni was formed through aheating operation by degassing this purple sample under high vacuum at100° C. for 24 hours. Yield: 85% based on ligand.

Powder X-Ray Diffraction Experiments

Powder X-ray diffraction experiments were carried out using aPANalytical Empyrean diffractometer equipped with a PIXcel3D detectoroperating in the scanning line detector mode with an active length of 4utilizing 255 channels. Cu K_(α12) radiation was used for thediffraction experiments.

Single-Gas Sorption Experiments

Micromeritics Tristar II 3030 and 3 Flex 3500 instruments were used forcollecting the sorption isotherms at 77 K for N₂ and 273 or 298 K forC₂H₂, C₂H₄, C₂H₆ and CO₂. A 4 L Dewar filled with liquid N₂ was adoptedfor temperature control at 77 K. Precise control of 273 and 298 K wererealized by a Julabo ME (v.2) with a recirculating control systemcontaining a mixture of ethylene glycol and water. Before adsorptionanalysis, MeOH-exchanged samples were fully degassed under high vacuum(<0.5 mmHg) at different conditions: TIFSIX-2-Cu-i (40° C. for 16hours), SIFSIX-3-Ni (100° C. for 24 hours) and Zn-atz-ipa (120° C. for18 hours). The apparent BET surface areas of Zn-atz-ipa andTIFSIX-2-Cu-i were determined from 77 K N₂ adsorption isotherms. 273 KCO₂ adsorption isotherms were used to calculate BET surface area forSIFSIX-3-Ni as N₂ is unable to diffuse readily into narrow pores ofSIFSIX-3-Ni at 77 K and CO₂ can fill the pore channel even at 273 K. Atevery interval of two independent isotherms for any material, thesorbent was regenerated by 5 hours degassing under high vacuum at 30° C.before commencement of the next sorption experiment.

Dynamic Breakthrough Experiments

In a three-gas breakthrough experiment, ca. 0.85 g of pre-activatedsingle sample, tandem-packed or mixed samples was placed in quartztubing (8 mm diameter) to form a fixed bed.

The adsorbent bed was purged under a 25 cm³/min flow of He gas at 90° C.for 1 hour before the breakthrough experiment. Upon cooling to 25° C., a2.1 cm³/min gas mixture containing 33.3% C₂H₂, 33.3% C₂H₄ and 33.3% C₂H₆gas was introduced. The outlet composition was continuously monitored bymass spectrometry (MS) until complete breakthrough was achieved. Whenoutlet composition of four gases reaches equilibrium, gas mixture flowwas then shut off and a gas flow (10 cm³/min) of He gas was introducedto regenerate the adsorption bed at <60° C. In order to examine thesorbent material performance at practical conditions, a 1.4 cm³/min gasmixture containing 1% C₂H₂, 49.5% C₂H₄ and 49.5% C₂H₆ gas was also usedduring breakthrough studies for four gas mixture.

In a four-gas breakthrough experiment, ca. 1.47 g of pre-activatedtandem-packed or mixed samples were placed in quartz tubing (8 mmdiameter) to form a fixed bed. Two different gas mixtures having thefollowing compositions: 25% C₂H₂/25% C₂H₄/25% C₂H₆/25% CO₂ and 1%C₂H₂/33% C₂H₄/33% C₂H₆/33% CO₂ were introduced at 2.8 cm³/min.

In recycling tests, the sample was regenerated after each experimentunder He flow of 10 cm³/min at 60° C. for ca. one hour or until thedisappearance of C₂ hydrocarbon and CO₂ signals in MS.

Pure Gas Adsorption Measurements

To evaluate the aforementioned sorbents for C₂H₄ separation processes,the pure gas adsorption properties of each sorbent were investigated.

Each sorbent was synthesized according to the methods described above.To verify purity, powder X-ray diffraction patterns and sorption data atcryogenic temperatures were performed on as-synthesized materials afteractivation (as shown in FIGS. 1 and 2). Single-gas isotherms at 273 and298 K were collected to 1 bar for TIFSIX-2-Cu-i, SIFSIX-3-Ni andZn-atz-ipa. As revealed by FIG. 3B, at 298 K and 1 bar, TIFSIX-2-Cu-iexhibits less uptake for C₂H₆ (2.1 mmol/g) than C₂H₄ (2.6 mmol/g), CO₂(4.3 mmol/g) and C₂H₂ (4.1 mmol/g). C₂H₂ exhibits the highest uptakefrom 0-0.8 bar for TIFSIX-2-Cu-i. In the case of SIFSIX-3-Ni, CO₂exhibits the highest uptake at 298 K and below 0.2 bar (FIG. 3C). ForZn-atz-ipa, all four gases show very similar uptake (1.8-2.0 mmol/g) at1 bar and 298 K (FIG. 3A). However, from 0-0.4 bar, higher uptake forC₂H₆ vs. CO₂, C₂H₂ and C₂H₄ was measured.

Isotherms at 298K were also collected for Zn-datz-ipa, MET-2, MET-5 andMET-6, as shown in FIGS. 22-25. All of these materials show higheruptake for C₂H₆ over C₂H₂, C₂H₄ and CO₂. For the MET materials, C₂H₆uptakes are higher than for other gases over 0-1 bar pressure range. Inparticular, MET-2 shows a much higher C₂H₆ uptake of 1.6 mmol/g at 298 Kand 1 bar than C₂H₄ of 1.2 mmol/g, C₂H₂ of 1.2 mmol/g and CO₂ of 1.1mmol/g.

To quantify the interaction strength between each gas and the respectiveframeworks, 273 and 298 K sorption data were fitted by the virialequation (FIGS. 4 to 9). The isosteric heat of adsorption (Q_(st)) wasthen calculated based on the Clausius—Clapeyron equation. Q_(st) valuesat low loading of four gases in TIFSIX-2-Cu-i, SIFSIX-3-Ni andZn-atz-ipa are compared in FIG. 10. Full Q_(st) curves for the fourgases in the three ultramicroporous sorbents are given in FIGS. 11 to 13and summarized in Table 1.

TABLE 1 S_(BET) ^(a) 298K uptake^(b) Low loading Q_(st) ^(c) IASTselectivity^(d) C₂H₂ C₂H₄ C₂H₆ CO₂ C₂H₂ C₂H₄ C₂H₆ CO₂ CO₂/C₂H₂ CO₂/C₂H₄CO₂/C₂H₆ SIFSIX-3-Ni 230 2.73/3.59 0.52/1.98 0.32/1.53 2.60/2.70 36.731.7 23.7 50.9 6.9 103 308 C₂H₂/C₂H₄ C₂H₂/C₂H₆ C₂H₂/CO₂ TIFSIX-2-Cu-i685 3.69/4.38 1.47/2.75 1.0/2.2 2.60/4.27 46.3 35.9 34.5 35.8 48.8 97.86.1 C₂H₆/C₂H₂ C₂H₆/C₂H₄ C₂H₆/CO₂ Zn-atz-ipa 650 1.43/1.99 1.37/1.801.53/1.81 0.98/1.90 37.5 40.0 45.8 31.5 2 1.7 5 ^(a)calculated from 77KN₂ and 273K CO₂ sorption (m²/g); ^(b)uptake at 0.25/1 bar and 298K(mmol/g); ^(c)Q_(st) at zero loading (kJ/mol); ^(d)calculated at 298Kand 1 bar of total pressure from binary gas mixture with 1:1 ratio.

As can be seen in Table 1, each sorbent material exhibits strongselectivity for one gas over the other three according to Q_(st): CO₂for SIFSIX-3-Ni (50.9 kJ/mol), C₂H₆ for Zn-atz-ipa (45.8 kJ/mol) andC₂H₂ for TIFSIX-2-Cu-i (46.3 kJ/mol) (see dashed line in FIG. 10H). Thismeans that, at least in principle, CO₂, C₂H₂ and C₂H₆ in a four-gasmixture including C₂H₄, will be preferably captured in SIFSIX-3-Ni,TIFSIX-2-Cu-i and Zn-atz-ipa, respectively.

Column Breakthrough Experiments

Dynamic breakthrough experiments at 298 K were conducted on acustom-built apparatus (FIG. 14) using an equimolar 3-component gasmixture of C₂H₂/C₂H₄/C₂H₆ and a total pressure of 1 bar. Controlexperiments using sorbent beds filled solely with TIFSIX-2-Cu-i andZn-atz-ipa were performed. C₂H₂ was selectively captured, but C₂H₄ andC₂H₆ were not separated by TIFSIX-2-Cu-i (FIG. 15A). For Zn-atz-ipa, asimilar problem occurred (FIG. 15B), but for C₂H₂/C₂H₄, C₂H₆ wasselectively adsorbed for ca. 10 minutes before breakthrough. However, a2-component (tandem) sorbent bed comprising TIFSIX-2-Cu-i andZn-atz-ipa, cleanly removed both C₂H₂ and C₂H₆ with C₂H₄ at >99.9%purity in the effluent stream (FIG. 15C).

By increasing the mass ratio of Zn-atz-ipa over TIFSIX-2-Cu-i from 1/1to 10/1, breakthrough times of C₂H₂ and C₂H₆ were optimized for theproduction of pure C₂H₄ using the 2-component sorbent material (FIGS.15E and 16 to 19). In the case of the 10/1 ratio, C₂H₂ and C₂H₆ wereobserved to breakthrough simultaneously, suggesting that the adsorptioncapacities of the two adsorbents had been fully utilized.

The 4-component equimolar mixture of C₂H₂/C₂H₄/C₂H₆/CO₂ was studiedafter adding SIFSIX-3-Ni to make a 3-component sorbent bed. Aftercomparing the CO₂ uptake of SIFSIX-3-Ni with those of C₂H₂ and C₂H₆ inthe single-gas adsorption studies, a ratio of 1/1.25/10 (TIFSIX-2-Cu-i:120 mg; SIFSIX-3-Ni: 150 mg; Zn-atz-ipa: 1.2 g) was adopted.Breakthrough results reveal that CO₂, C₂H₆ and C₂H₂ were captured (FIG.15F) as polymer-grade C₂H₄ was harvested in the effluent stream (workingcapacity 0.14 mmol/g). After regeneration (<60° C.) under He gas flow(10 ml/min, 1 hour), the sorbent bed was reused; performance wasunaffected after 9 such cycles (FIG. 20).

Sorbent recycling tests for each adsorbent (i.e. CO₂ for SIFSIX-3-Ni,C₂H₂ for TIFSIX-2-Cu-i and C₂H₆ for Zn-atz-ipa) were conducted in orderto verify ease of recyclability and revealed no capacity loss after 10cycles. To address the energy footprint of the SSST columns, temperatureprogrammed desorption (TPD) experiments were conducted for eachindividual adsorbent and all tandem packed columns after four-gasmixture breakthroughs. Sorbent bed regeneration was achieved with aregeneration temperature of only 60° C. This low regenerationtemperature fulfils the promise offered by physisorbents.

TABLE 2 Packing Time for removal after breakthrough^(a) (mins)Regeneration order C₂H₂ C₂H₄ C₂H₆ CO₂ condition A-C-B 44.6 48.3 30.973.0 60° C., He (20 ml/min) B-C-A 46.4 48.9 31.5 93.2 60° C., He (20ml/min) A-B-C 81.2 81.6 47.7 78.8 60° C., He (20 ml/min) C-B-A 75.1 80.141.1 90.0 60° C., He (20 ml/min) B-A-C 75.3 60.2 40.9 80.0 60° C., He(20 ml/min) C-A-B 44.7 44.5 43.1 49.2 60° C., He (20 ml/min) A 22.5 28.323.7 49.4 60° C., He (20 ml/min) B 66.8 71.7 26.5 30.3 60° C., He (20ml/min) C 30.4 46.2 35.6 29.7 60° C., He (20 ml/min) Single Run^(b)Regeneration adsorbent 1 2 3 4 5 6 7 8 9 condition A-CO₂ 109.7 109.7109.7 109.6 109.6 109.5 109.6 109.6 109.7 60° C., N₂ (20 ml/min) B-C₂H₂108.0 108.1 108.2 108.3 108.2 108.2 108.0 108.0 108.1 60° C., N₂ (20ml/min) C-C₂H₆ 104.7 104.7 104.6 104.6 104.5 104.5 104.5 104.5 104.4 60°C., N₂ (20 ml/min) A: SIFSIX-3-Ni; B: TIFSIX-2-Cu-i; C: Zn-atz-ipa

a: Ending time (mins) for each gas releasing from post-breakthroughcolumn under regeneration condition, is considered as the time at whichthe outlet concentration reaches less than 1% of initial concentration;b: Uptake (weight percentages of saturated adsorbent, assuming theactivated adsorbent as 100%) for each adsorbent at the end of eachadsorption cycle (adsorption at 30° C. under corresponding gas flow),whereas desorption follows at 60° C. under N₂flow.

In industrial C₂ hydrocarbon gas streams, acetylene typically makes uponly around 1 wt % of the total flow. In order to examine theperformance of the sorbent materials with more industrially relevant andchallenging gas mixtures, C₂H₂/C₂H₄/C₂H₆ (1/49.5/49.5) andC₂H₂/C₂H₄/C₂H_(6/)CO₂ (1/33/33/33) were tested.

Polymer-grade C₂H₄ with working capacities of 0.32 and 0.10 mmol/g washarvested from gas mixtures of 1/49.5/49.5 and 1/33/33/33, respectively(FIG. 15D and 21). The higher partial pressure of C₂H₆ in the1/49.5/49.5 gas mixture contributes to the higher working capacity forC₂H₄ production with more C₂H₆ molecules being captured at higherpartial pressures (0.495 vs 0.33 bar) by Zn-atz-ipa. 0.33 bar) byZn-atz-ipa.

To explore how performance is affected by packing in a combinationsorbent bed, we mixed 120 mg of TIFSIX-2-Cu-i and 1200 mg of Zn-atz-ipato generate a physical mixture and tested its performance. Breakthroughdata for an equimolar gas mixture of C₂H₂/C₂H₄/C₂H₆ reveals that C₂H₂was not effectively removed before C₂H₄ breakthrough. Further, the C₂H₆concentration was not reduced to the required specification (i.e.<0.1%).

The effect of packing order on performance was assessed with sixparallel columns and breakthrough experiments using a 1/1/1/1 gasmixture at 298 K and 1 bar. The results showed that with the sorbentsarranged in sequence in the following order (with respect to the flow ofthe gaseous composition) SIFSIX-3-Ni : Zn-atz-ipa : TIFSIX-2-Cu-i, thehighest working capacity was obtained (0.14 mmol/g). Generally, improvedpurifications were obtained when the Zn-atz-ipa was used as the first orsecond sorbent. The effects of different selectivity values, kineticsand co-adsorption are likely to be the cause of this observation.Particle size and amount of sorbent used was found to have littleeffect, with smaller particle size and larger sample amounts resultingin a slightly improved C₂H₄ purification. Columns with tighter packingprovided improved performance.

Further Examples

Synthesis of [Ni₂(bpy)₂(L-tart)F₂]—an Alternative C₂H₂ Selective Sorbentto TIFSIX-2-Cu-i

L-tartaric acid (31 mg, 0.2 mmol), NiF₂.4H₂O (67 mg, 0.4 mmol), LiF (37mg, 1.5 mmol) and 4,4′-bipyridine (60 mg, 0.4 mmol) were mixed in H₂O(10 mL). This reaction mixture was capped in a 22 mL borosilicate vialand heated at 120° C. for 24 hours. After heating, the mixture wasfiltered and washed with water, the green powder was harvested. Yield:77 mg.

Characterization of [Ni₂(bpy)₂(L-tart)F₂]

[Ni₂(bpy)2(L-tart)F₂] is isostructural to the [Co₂F₂(bpy)₂(L-tart)] aspreviously reported [Zhang, G.; Hu, H.; Li, H.; Zhao, F.; Liu, Y.; He,X.; Huang, H.; Xu, Y.; Wei, Y.; Kang, Z., Homochiral metal-organicporous materials for enantioselective recognition and electrocatalysis,CrystEngComm 2013, 15(17), 3288-3291]. The phase purity ofas-synthesized [Ni₂(bpy)₂(L-tart)F₂] was confirmed by PXRD (FIG. 26).FIG. 26 shows the calculated powder X-ray powder diffraction pattern of[Co₂F₂(bpy)₂(L-tart)] and measured powder X-ray diffraction pattern ofas-synthesized [Ni₂(bpy)₂(L-tart)F₂]. When heated in nitrogen flow,[Ni₂(bpy)₂(L-tart)F₂] maintained crystallinity up to ca. 200° C. (FIG.27). FIG. 27 shows variable temperature powder X-ray diffractionpatterns of [Ni₂(bpy)₂(L-tart)F₂] measured in nitrogen flow.

Sorption Properties of [Ni₂(bpy)₂(L-tart)F₂]

[Ni₂(bpy)₂(L-tart)F₂] exhibits permanent porosity as demonstrated bynitrogen sorption at 77K (FIG. 28). FIG. 28 shows a 77 K N₂ sorptionisotherm of [Ni₂(bpy)₂(L-tart)F₂]. Single component isotherms collectedat 298K on [Ni₂(bpy)₂(L-tart)F₂] demonstrate that the uptake of C₂H₂ ishigher than the other gases tested (FIG. 29). FIG. 29 shows adsorptionof CO₂ (squares), C₂H₂ (stars), C₂H₁₄ (triangles), and C₂H₆ (circles) at298 K for [Ni₂(bpy)₂(L-tart)F₂].

A comparison of key sorption parameters of [Ni₂(bpy)₂(L-tart)F₂] andTIFSIX-2-Cu-i can be found in Table 3 and FIG. 30. IAST selectivitycalculations indicate that [Ni₂(bpy)₂(L-tart)F₂] can be used as theselective C₂H₂ sorbent for SSST and is an alternative to TIFSIX-2-Cu-i.FIG. 30 shows selectivity of C₂H₂/C₂H₄, C₂H₂/C₂H₆ and C₂H₂/CO₂calculated for equimolar binary mixture at 298 K and 1 bar of totalpressure from Ideal Adsorbed Solution Theory (IAST) in[Ni₂(bpy)₂(L-tart)F₂].

TABLE 3 Key sorption parameters of [Ni₂(bpy)₂(L-tart)F₂] andTIFSIX-2-Cu-i. 298K uptake^(a) IAST selectivity^(b) C₂H₂ C₂H₄ C₂H₆ CO₂C₂H₂/C₂H₄ C₂H₂/C₂H₆ C₂H₂/CO₂ TIFSIX-2-Cu-i 3.69/4.38 1.47/2.75 1.0/2.22.60/4.27 48.8 97.8 6.1 [Ni₂(bpy)₂(L-tart)F₂] 3.44/4.1  0.3/1.00.03/0.14 0.17/1.71 86 10000+    237 ^(a)uptake at 0.25/1 bar and 298K(mmol/g); ^(b)calculated at 298K and 1 bar of total pressure from binarygas mixture with 1:1 ratio.

Synthesis of [Co₂(bpy)₂(Tzba)F₂]—an Alternative C₂H₆ Adsorbent toZn-atz-ipa

4-(1H-Tetrazol-5-yl) benzoic acid (herein referred to as Tbza) (72 mg,0.38 mmol), 4,4′-bipyridine (47 mg, 0.3 mmol) and Co(NO₃)₂.6H₂O (87 mg,0.3 mmol) were combined in a mixture of DMF (3 ml), ethanol (6 ml) andH₂O (12 ml) and 6 drops of HBF₄. This reaction mixture was then cappedin a 22 mL borosilicate vial and heated at 120° C. for 24 hours. Afterheating, the mixture was filtered and washed with water, the redcrystalline powder was harvested. Yield: 65 mg.

Characterization of [Co₂(bpy)₂(Tzba)F₂]

The structure of [Co₂(bpy)₂(Tzba)F₂] is illustrated in FIG. 31 and wasdetermined by single crystal X-ray diffraction data collected on aBruker D8 diffractometer using multilayer monochromated Mo-Kα radiation(λ=0.71073 Å). FIG. 31 shows the coordination environment of[Co₂(bpy)₂(Tzba)F₂] from single crystal data and a packing diagram of[Co₂(bpy)₂(Tzba)F₂]. An Oxford Cryosystems Cryostream 700 Plus was usedto maintain the temperature of the crystal at 298 K throughout the datacollection. Data reduction was carried out using the Bruker softwarepackage SAINT.¹ Absorption corrections and other systematic errors wereaccounted for using SADABS.² The structure was solved by direct methodsusing SHELXS and refined using SHELXL.³ X-Seed⁴ was used as a graphicalinterface for the SHELX program suite. Hydrogen atoms were placed incalculated positions using riding models. The coordination environmentin [Co₂(bpy)₂(Tzba)F₂] comprises two cobalt metal centres, one TzBaligand, two bpy ligands and two fluoride anions that bridge neighbouringmetal centres. The TzBa ligand chelates two metal centres in analternating fashion, first through the tetrazole moiety and then throughthe dicarboxylic acid moiety. This non-interpenetrated 3D MOF containsguest accessible channels of approximately 38% (FIG. 31 right).

Phase purity of as-synthesized [Co₂(bpy)₂(Tzba)F₂] was confirmed by PXRD(FIG. 32). FIG. 32 shows calculated powder X-ray diffraction patterns of[Co₂(bpy)₂(Tzba)F₂] from single crystal data and measured powder X-raydiffraction patterns of as-synthesized [Co₂(bpy)₂(Tzba)F₂]. When heatedunder nitrogen flow, [Co₂(bpy)₂(Tzba)F₂ retains crystallinity up to ca.190° C. (FIG. 33). FIG. 33 shows a thermogravimetric analysis trace of[Co₂(bpy)₂(Tzba)F₂] measured under nitrogen flow.

Sorption Properties of [Co₂(bpy)₂(Tzba)F₂]

[Co₂(bpy)₂(Tzba)F₂] exhibits permanent porosity as demonstrated bysorption of various gases at 298K. Single component isotherms collectedat 298K on [Co₂(bpy)₂(Tzba)F₂] demonstrate high preferential C₂H₆ uptakevs C₂H₄ (FIGS. 34 and 35). FIG. 34 shows the adsorption of CO₂(squares), C₂H₂ (stars), C₂H₄ (triangles), and C₂H₆ (circles) at 298 Kfor [Co₂(bpy)₂(Tzba)F₂]. FIG. 35 shows the selectivity of C₂H₆/C₂H₄,C₂H₆/CO₂ and C₂H₆/C₂H₂ calculated for binary mixtures at 298 K and 1 barof total pressure from Ideal Adsorbed Solution Theory (IAST) in[Co2(bpy)2(Tzba)F2].

Comparison of key sorption parameters of [Co₂(bpy)₂(Tzba)F₂] andZn-atz-ipa are given in Table 5. IAST selectivity calculations indicatethat [Co₂(bpy)₂(Tzba)F₂] can be used as the C₂H₆ selective sorbent in anSSST process, thus serving an alternative to Zn-atz-ipa.

TABLE 5 Sorption data summary of [Co₂(bpy)₂(Tzba)F₂] and Zn-atz-ipa.298K uptake^(a) IAST selectivity^(b) C₂H₂ C₂H₄ C₂H₆ CO₂ C₂H₆/C₂H₄C₂H₆/C₂H₂ C₂H₆/CO₂ Zn-atz-ipa 1.43/1.99 1.37/1.80 1.53/1.81 0.98/1.901.7 2 5 [Co₂(bpy)₂(Tzba)F₂] 1.4/2.1 0.7/1.2 1.2/1.6 2.6/4.2 3.8 0.6 11.6^(a)uptake at 0.25/1 bar and 298K (mmol/g); ^(b)calculated at 298K and 1bar of total pressure from equimolar binary gas mixtures.

REFERENCES

1. SAINT Data Reduction Software, Version 6.45; Bruker AXS Inc.,Madison, Wisc., 2003.

2. (a) SADABS, Version 2.05; Bruker AXS Inc., Madison, Wisc., 2002; (b)Blessing, R. H. An Empirical Correction for Absorption Anisotropy. ActaCryst. 1995, A51, 33-38.

3. Sheldrick, G. M. A Short History of SHELX. Acta Cryst. 2008, A64,112-122.

4. Barbour, L. J. X-Seed — A Software Tool for SupramolecularCrystallography. J. Supramol. Chem. 2001, 1, 189-191.

In summary, the present invention provides a single-step method ofobtaining a target gas, such as ethylene, methane, propane or propylene,from a gaseous mixture by contacting the gaseous mixture with a sorbentmedia containing a sorbent media adapted for removal of each gaseousimpurity in the gaseous mixture. In particular, the sorbent media of thepresent invention comprising the sorbent materials described hereinprovides a one-step C₂H₄ purification. Polymer-grade C₂H₄ was producedin one-step from tertiary (C₂H₂/C₂H₄/C₂H₆) and quaternary(C₂H₂/C2H₄/C₂H₆/CO₂) gas mixtures which mimic those currently producedin industrial processes which are currently separated using multi-stepenergy intensive methods.

1. A method of obtaining a target gas from a gaseous compositioncomprising the target gas, a first gas and a second gas, the methodcomprising the step of contacting the gaseous composition with a sorbentmedia to remove at least some of the first gas and at least some of thesecond gas from the gaseous composition; wherein the sorbent mediacomprises a first sorbent material and a second sorbent material;wherein the first sorbent material has a higher adsorption selectivityfor the first gas than for the target gas; and wherein the secondsorbent material has a higher adsorption selectivity for the second gasthan for target gas.
 2. The method according to claim 1, wherein thetarget gas is ethylene, propylene, propane or methane.
 3. The methodaccording to any preceding claim, wherein the first gas is acetylene andthe second gas is ethane.
 4. The method according to any preceding claimwherein the first sorbent material is an ultramicroporous materialhaving a three-dimensional lattice of metal species (M) and linkergroups; wherein the metal species (M) are linked together in a first andsecond dimension by first linker groups (L¹) and are linked together ina third dimension by second linker groups (L²) to form thethree-dimensional lattice; and wherein one of L¹ and L² is an organiclinker group and the other of L¹ and L² is either an inorganic or anorganic linker group; and wherein the ultramicroporous material has theformula M_(x)(L¹)₂(L²)Y_(z) wherein x=1 to 3, Y is an inorganic anionand z=0 to
 3. 5. The method according to claim 4, wherein M is Cu²⁺, L¹is 4,4′-bipyridylacetylene and L² is TiF₆ ²⁻.
 6. The method according toclaim 4, wherein M is Ni²⁺, L¹ is 4,4′-bipyridine and L² is tartaricacid, preferably L-tartaric acid.
 7. The method according to anypreceding claim, wherein the second sorbent material is anultramicroporous material of formula Zn₂(A)₂(B); wherein A is anamino-substituted heterocyclic ligand and B is a dicarboxylate ligand,preferably wherein the second gas is ethane.
 8. The method according toclaim 7, wherein A is an ion derived from 3-amino-1,2,4-triazole and Bis an ion derived from isophthalic acid.
 9. The method according to anyone of claims 1 to 6, wherein the second sorbent material is anultramicroporous material of formula M_(x)(L¹)₂(L²)Y_(z) wherein M isCo²⁺ or Ni²⁺, wherein x is an integer from 1 to 3, L¹ is an organiclinker group, L² is a di-carboxylic acid linker or a di-carboxylic acidequivalent linker having an azolate group, Y is an inorganic anion and zis an integer from 0 to 3, preferably wherein the second sorbent is[Co₂(bpy)₂(Tzba)F₂], preferably wherein the second gas is ethane. 10.The method according to any preceding claim, wherein the gaseouscomposition comprises a third gas, as an impurity; and wherein thesorbent media comprises a third sorbent material which has a higheradsorption selectivity for the third gas than for the target gas;preferably wherein the third gas is carbon dioxide and the target gas isethylene.
 11. The method according to claim 10 wherein the third sorbentmaterial is an ultramicroporous material of formula M(L¹)₂(L²); whereinM is Ni, L¹ is pyrazine and L² is SiF₆ ²⁻.
 12. The method according toany preceding claim, wherein the target gas is obtained with a purity ofat least 99 wt %, suitably at least 99.9 wt %.
 13. The method accordingto any preceding claim, wherein the contacting of the gaseouscomposition with the sorbent media is carried out at a pressure of from0.5 to 2 bar and a temperature of from 0° C. to 40° C.
 14. A method ofremoving ethane from a gaseous composition, the method comprising thestep of contacting the gaseous composition with a sorbent material toremove at least some of the ethane, wherein the sorbent materialcomprises an ultramicroporous material of formula Zn₂(A)₂(B); wherein Ais an amino-substituted heterocyclic ligand and B is a dicarboxylateligand; or wherein the sorbent material comprises an ultramicroporousmaterial of formula M_(x)(L¹)₂(L²)Y_(z) wherein M is Co²⁺ or Ni²⁺,wherein x is an integer from 1 to 3, L¹ is an organic linker group, L²is a di-carboxylic acid linker or a di-carboxylic acid equivalent linkerhaving an azolate group, Y is an inorganic anion and z is an integerfrom 0 to
 3. 15. The method according to claim 14, wherein the sorbentmaterial is Zn₂(atz)₂(ipa) or [Co₂(bpy)₂(Tzba)F₂].
 16. A method ofremoving acetylene from a gaseous composition, the method comprising thestep of contacting the gaseous composition with a sorbent material toremove at least some of the acetylene, wherein the sorbent materialcomprises an ultramicroporous material of formula M_(x)(L¹)₂(L²)Y_(z)wherein the metal species (M) is selected from atoms or ions of Co, Cu,Zn and Ni, wherein x is an integer from 1 to 3, L¹ is a two-connectednitrogen ligand, L² is a dicarboxylic acid, Y is an anion and z is aninteger from 0 to
 3. 17. The method according to claim 16, wherein L² isselected from chiral or racemic tartaric acid, malic acid, succinicacid, fumaric acid, 2,3-dibromosuccinic acid, aspartic acid,1,4-benzenedicarboxylic acid and 1,3-benzenedicarboxylic acid.
 18. Themethod according to claim 17, wherein the ultramicroporous material is[Ni₂F₂(bpy)₂(L-tart).
 19. A sorbent media comprising a first sorbentmaterial and a second sorbent material; wherein the first sorbentmaterial has a higher adsorption selectivity for the first gas than forthe target gas; wherein the second sorbent material has a higheradsorption selectivity for the second gas than for the target gas; andwherein the first sorbent material and the second sorbent material aredifferent ultramicroporous materials.
 20. An apparatus for obtaining atarget gas from a gaseous composition comprising a target gas, a firstgas and a second gas, the apparatus comprising a sorbent media accordingto claim
 19. 21. Use of an ultramicroporous material to separate ethanefrom a gas mixture comprising ethane; wherein the ultramicroporousmaterial has a formula of either: Zn₂(A)₂(B) wherein A is anamino-substituted heterocyclic ligand and B is a dicarboxylate ligand;or M_(x)(L¹)₂(L²)Y_(z) wherein M is Co²⁺ or Ni²⁺, wherein x is aninteger from 1 to 3, L¹ is an organic linker group, L² is adi-carboxylic acid linker or a di-carboxylic acid equivalent linkerhaving an azolate group, Y is an inorganic anion and z is an integerfrom 0 to 3; preferably wherein the ultramicroporous material isZn₂(atz)₂(ipa) or [Co₂(bpy)₂(Tzba)F₂].
 22. Use of an ultramicroporousmaterial of formula M_(x)(L¹)₂(L²)Y_(z) to separate acetylene from a gasmixture comprising acetylene, wherein the metal species (M) is selectedfrom atoms or ions of Co, Cu, Zn and Ni, wherein x is an integer from 1to 3, L¹ is a two-connected nitrogen ligand, L² is a dicarboxylic acid,Y is an anion and z is an integer from 0 to
 3. 23. The use according toclaim 22, wherein L² is selected from chiral or racemic tartaric acid,malic acid, succinic acid, fumaric acid, 2,3-dibromosuccinic acid,aspartic acid, 1,4-benzenedicarboxylic acid and 1,3-benzenedicarboxylicacid.
 24. The use according to claim 23, wherein the ultramicroporousmaterial is [Ni₂F₂(bpy)₂(L-tart).
 25. An ultramicroporous material offormula [Co₂(bpy)₂(Tzba)F₂].